A common type of fire collar comprises a metal collar which is fastened around a concrete slab-penetrating plastics material pipe in the region where it traverses the slab; the collar enclosing an intumescent material. When a fire on one side of the concrete slab reaches a sufficient intensity to melt the pipe where it penetrates the slab, it also causes the intumescent material to expand and seal off the void left by the melted pipe. In this way, a barrier is formed to prevent the spread of the fire to the other side of the concrete slab.
A major problem with this type of fire collar is that the time taken for the intumescent material to form a seal can be too long in rapidly advancing fires with the result that the fire can still spread to the other side of the partition.
A recent attempt to overcome this problem is a fire damper comprising a tubular insert having a grid of intumescent material formed across the circumference of the pipe or duct. However, although such an arrangement enables very quick sealing to occur, it has the disadvantage that it slows down the passage of fluid along the pipe or duct. Such a slowdown is amplified by the number of concrete slabs which the pipe or duct traverses to the extent that complete blockage of the fluid can ultimately occur.